Effects of increasing levels of corn dried distillers grains with solubles and monensin on ruminal biohydrogenation and duodenal flows of fatty acids in beef heifers fed high-grain diets.

Corn dried distillers grains with solubles (DDGS) contains high crude fat and is reported to confer to PUFA some degree of protection from ruminal biohydrogenation (BH). There is also indication that inclusion in diets of high energy feed such as DDGS results in a reduced response to monensin in feedlot cattle. This study was conducted to determine the effects of increasing corn DDGS inclusion and monensin on ruminal BH and duodenal flows of fatty acid (FA). Five ruminally and duodenally cannulated Angus heifers (initial BW, 556 ± 36 kg) were assigned to a 5 × 5 Latin square with 2 × 2 + 1 factorial arrangement. Treatments were control (CON; 10% barley silage, 87.8% barley grain, 2.2% mineral and vitamin supplement, and 28 mg monensin/kg DM) and diets substituting 20% (LDG) or 40% (HDG) corn DDGS for barley grain combined with 28 (ML) or 48 mg (MH) monensin/kg diet DM: 1) CONML, 2) LDGML, 3) LDGMH, 4) HDGML, and 5) HDGMH. Intakes of total and individual FA increased (P < 0.01) with inclusion of DDGS in the diet and tended (P = 0.10) to be less for heifers fed MH than ML diets. Overall, there was no interaction between levels of DDGS and monensin on ruminal BH, flows of FA to duodenum, and intestinal digestibility. Flows (g/d) of CLA c9,t11, α-linolenic acid (C18:3n-3), MUFA, and PUFA to the duodenum were linearly increased (P < 0.01) with increasing DDGS inclusion. However, increased monensin trended to decrease the flows of linoleic acid (C18:2 c9 c12; P = 0.07), α-linolenic acid (P = 0.07), and MUFA (P = 0.08) and decreased that of PUFA (P = 0.05). Ruminal BH of unsaturated FA (USFA), PUFA, and C18:2 c9,c12 did not differ among treatments. The FA profiles in the duodenal digesta were not different except for the percentage of CLA c9,t11, which tended (P = 0.06) to linearly increase with increasing DDGS such that it was greater (P = 0.04) for HDG than for the LDG diet. Additionally, the percentage of CLA t10,c12 linearly (P < 0.01) increased with increasing DDGS inclusion. Intestinal digestibility of SFA (P < 0.01), USFA (P = 0.05), and total FA (P = 0.01) was greater for heifers fed HDG than heifers fed LDG diets. These results indicate that increasing corn DDGS in finishing diet increases the provision of PUFA to feedlot cattle due to increased intake and flows of PUFA to the duodenum. Increasing supplementation of monensin from 28 to 48 mg/kg DM had no effect on ruminal BH and intestinal digestibility of FA but decreased intake and duodenal flows of FA.